The present invention relates generally to the preservation of biological matter comprising tissue for transplantation or other purposes and relates more particularly to the preservation of biological matter comprising tissue using fluid perfusion.
Transplantation of islets of Langerhans has been investigated for its potential as a treatment for type 1 diabetes mellitus for over 30 years since the allotransplantation of islets from rats was shown to reverse chemically induced diabetes (see Ballinger et al., “Transplantation of intact pancreatic islets in rats,” Surgery, 72(2):175-86 (1972), which is incorporated herein by reference). Several years later, it was shown that auto-transplantation of islets back to a donor was a feasible treatment to prevent the onset of diabetes in people with pancreatitis (see Najarian et al., “Total or near total pancreatectomy and islet autotransplantation for treatment of chronic pancreatitis,” Ann Surg., 192(4): 526-42 (1980), which is incorporated herein by reference). Successful islet allotransplantation, however, remained difficult to achieve until 2000 when the development of the Edmonton Protocol achieved success in seven consecutive patients transplanted with islets from multiple pancreata (see Shapiro et al., “Islet transplantation in seven patients with type I diabetes mellitus using a glucocorticoid-free immunosuppressive regimen, New England Journal of Medicine, 343(4):230-8 (2000), which is incorporated herein by reference). The aforementioned success has largely been attributed to the use of a glucocorticoid-free immunosuppression. This success was then repeated at other institutions, including the University of Minnesota, with over 500 transplants utilizing variations of the Edmonton Protocol worldwide from 2000-2006 (see Shapiro et al., “Edmonton's islet success has indeed been replicated elsewhere,” The Lancet, 362(9391), 1242 (2003); Emamaullee et al., “Factors influencing the loss of beta-cell mass in islet transplantation,” Cell Transplantation, 16(1):1-8 (2007), both of which are incorporated herein by reference). Islet transplantation offers several advantages over other presently utilized treatments for diabetes. Due to the innate ability of the islets to monitor and regulate glucose levels via insulin production, transplantation allows for the constant, tight control of blood glucose levels, something which cannot be achieved by patient self-monitoring. Even when tight glucose control is not fully achieved, islet transplantation is especially important in patients who exhibit hypoglycemia unawareness, the lack of physical symptoms indicative of low blood sugar. In addition, when compared to other transplant treatments, transplantation minimizes the chance of infection since the infusion of islets into the portal vein does not require open surgery.
Even though the use of islet transplantation for consistent diabetes reversal has been demonstrated, there still remain several hurdles for the widespread implementation of this therapy in a clinical setting. Although some success has been achieved with single donor transplants, most centers continue to require multiple donor organs for a single patient for various reasons including low islet yields and/or quality per donor (see Hering et al., “Single-donor, marginal-dose islet transplantation in patients with type I diabetes,” JAMA, 293(7):830-5 (2005), which is incorporated herein by reference). There is presently a shortage of quality donor organs, which limits the number of transplants possible. With increasing interest in islet transplantation and with new centers applying to the U.S. Food and Drug Administration (FDA) for Investigational New Drug (IND) status, it is more important than ever to maximize both the number and quality of available organs. In order to do this, it is necessary to protect the islets from damage beginning at the time of organ procurement and islet processing through eventual engraftment in the transplant recipient.
One of the main challenges of pancreatic islet transplantation is acquiring viable, functional transplant tissue in sufficient quantity for successful treatment (see Iwanaga et al., “Pancreas preservation for pancreas and islet transplantation, invited review, Current Opinion in Organ Transplantation, 13(2):135-141 (2008), which is incorporated herein by reference). As such, it is important to: (1) maximize the donor organs that are acceptable for clinical use; (2) improve the preservation, storage, and transport of those organs to keep them acceptable; and (3) enhance the yield and quality of the islets harvested from the organ by improvements in islet isolation, culture, and storage. There appears to be a critical mass of viable islets for the success of single donor transplants, and current protocols yield transplant tissue that is generally right at the marginal edge of this critical mass.
The current protocol for pancreas procurement includes brain-dead, heart-beating donors with practically no warm ischemia (WI) time. Pancreas preservation (including transport and storage times) must be equal to or less than eight hours of cold (4-8° C.) storage. The cold storage protocols vary, with some using established cold preservation solutions (CPS), such as UW (University of Wisconsin) solution, and with others using experimental CPS or combinations of CPS. Since 2002, the two-layer method (TLM) has drawn much attention. TLM was developed as a method of pancreas preservation in the late 1980's and early 1990's (see Kuroda et al., “A new simple method for cold-storage of the pancreas using perfluorochemical,” Transplantation, 46(3):457-60 (1988); Fujino et al., “Preservation of canine pancreas for 96 hours by a modified two-layer (UW solution/perfluorochemical) cold storage method,” Transplantation, 51(5):1133-5 (1991); Kuroda et al., “Oxygenation of the human pancreas during preservation by a two-layer (University of Wisconsin solution/perfluorochemical) cold-storage method,” Transplantation, 54(3):561-2 (1992), all of which are incorporated herein by reference).
TLM involves suspending a pancreas half-way between layers of CPS and oxygenated perfluorocarbon (PFC). The basic concept is to enhance tissue oxygenation during storage by supplying greater amounts of oxygen to the organ surface due to the enhanced oxygen carrying capacity of PFC as compared to CPS. TLM gained a lot of momentum as the state of the art for pancreas preservation in the early 2000's following the development of the Edmonton Protocol, with many islet processing centers publishing on the advantages of this approach to organ preservation when compared with classical methods (see Hering et al., “Impact of two-layer pancreas preservation on islet isolation and transplantation, Transplantation, 74(12):1813-6 (2002); Fraker et al., “Use of oxygenated perfluorocarbon toward making every pancreas count,” Transplantation, 74(12): 1811-2 (2002); Tsujimura et al., “Human islet transplantation from pancreases with prolonged cold ischemia using additional preservation by the two-layer (UW solution/perfluorochemical) cold-storage method,” Transplantation, 74(12):1687-91 (2002); Lakey et al., “Preservation of the human pancreas before islet isolation using a two-layer (UW solution-perfluorochemical) cold storage method,” Transplantation, 74(12):1809-11 (2002); Ricordi et al., “Improved human islet isolation outcome from marginal donors following addition of oxygenated perfluorocarbon to the cold-storage solution,” Transplantation, 75(9):1524-7 (2003); Matsumoto et al., “The effect of two-layer (University of Wisconsin solution/perfluorochemical) preservation method on clinical grade pancreata prior to islet isolation and transplantation,” Transplantation Proceedings, 36(4):1037-9 2004; Witkowski et al., “Two-layer method in short-term pancreas preservation for successful islet isolation,” Transplantation Proceedings, 37(8), 3398-401 (2005), all of which are incorporated herein by reference).
Much of the interest in TLM was due to the potential for use of marginal donor organs for successful transplantation. Presently, there is a shortage of suitable donor organs, and in some countries the use of heart-beating donors is prohibited due to cultural taboos. Recently, however, it has come to light that oxygenation that depends on surface diffusion, as is the case in TLM, may be insufficient to oxygenate the majority of the human pancreas. Diffusion modeling of the pancreas by a group at the University of Minnesota has demonstrated that oxygen can only penetrate the outer 1 mm of the pancreas (see Papas et al., “Pancreas oxygenation is limited during preservation with the two-layer method,” Transplantation Proceedings, 37(8), 3501-4 (2005), which is incorporated herein by reference). Additionally, several islet transplantation centers have very recently released retrospective data demonstrating that there is no significant improvement in islet isolation or transplantation outcome when the pancreas is preserved by TLM vs. classical storage in CPS (UW) alone (see Kin et al., “Islet isolation and transplantation outcomes of pancreas preserved with University of Wisconsin solution versus two-layer method using preoxygenated perfluorocarbon,” Transplantation, 82(10):1286-90 (2006); Caballero-Corbalan et al., “No beneficial effect of two-layer storage compared with UW-storage on human islet isolation and transplantation,” Transplantation, 84(7):864-9 (2007), both of which are incorporated herein by reference).
In view of the above, there clearly remains a compelling need for improved methods of pancreas preservation.
For other human organs, passive cold storage in CPS is common and reported in the peer-reviewed literature. There are also some published protocols and commercial equipment for liquid perfusion preservation of organs. In both of these methods, provision of oxygen is minimal and can be inadequate for optimal organ preservation.